Country superstar George Jones, known for "He Stopped Loving Her Today" and a long string of other hits, has died.

He was 81.

According to Webster & Associates, the Nashville public relations firm that represented Jones, he died Friday at Vanderbilt University Medical Center. He was hospitalized there on April 18 for treatment of a fever and irregular blood pressure, the p.r. firm adds.

His page on the website of the Country Music Hall of Fame says that, "many attempts have been made to capture in words the immense, singular vocal gifts that have made George Glenn Jones one of the most influential singers in country music history. He is the undisputed successor of earlier primitive geniuses such as Hank Williams and Lefty Frizzell—singers who, in turn, so heavily influenced him in his formative years."

"Born September 12, 1931, Jones is regarded among the most important and influential singers in American popular music history. He was the singer of enduring country music hits including 'She Thinks I Still Care,' 'The Grand Tour,' 'Walk Through This World With Me,' 'Tender Years' and 'He Stopped Loving Her Today,' the latter of which is often at the top of industry lists of the greatest country music singles of all time."

He had his first No. 1 hit in 1959, with "White Lightning."

He was once married to another country star and singing partner, Tammy Wynette. "In 1983," WSMV adds, "Jones married the former Nancy Ford Sepulvado. The union, he repeatedly said, began his rehabilitation from drugs and alcohol and prolonged his life."

Jones has made a career out of heartbreak and pain, but he says it's not who he is as a person.

"It's not that you're unhappy when you're doing ballads," Jones says. "It's just that I try to live the song. During that three minutes or whatever it is, you try to step in that person's shoes. It seems for some reason the words tell you right away that you know how they feel."

NPR's music team will have much more about Jones and his legacy later today.

CORNISH: A defining voice of country music is gone. George Jones died today in Nashville at age 81. He had hit songs going back to the 1950s, a voice that conveyed heartbreak better than anyone and an influence felt well beyond the boundaries of country music. Our co-host Melissa Block visited with George Jones a few years back and has this remembrance.

(SOUNDBITE OF MUSIC)

JONES: (Singing) Walk through this world with me, go where I go.

MELISSA BLOCK, HOST:

We visited at his estate south of Nashville and after our interview, sat for some pictures in white rocking chairs on his front porch. George Jones was impeccably turned out, with ostrich leather shoes and that famous perfectly coiffed swoop of silver hair. But here's what I remember best. All of a sudden, he made a goofy face, poking a piece of gum out of his mouth and cracking us all up.

His nickname was the possum.

JONES: I guess I look like a possum a little bit. I didn't like it at first, but then I kept looking in the mirror every morning. I said, good god, you got them little beady eyes. It don't bother me no more, though. They still - I said, well, just go right and call me whatever you want to.

BLOCK: When I talked with him in 2010, George Jones was still performing about 90 concert dates a year. Retirement was unthinkable.

JONES: We don't want to lay down and give up just 'cause we're old. Young people think we're crazy. Oh, one morning you'll wake up and look in the mirror like I did and say, what in the devil happened? Woo, where did it go? Oh, Lordy.

BLOCK: George Jones was the youngest of eight kids born in a log house in the big thicket, East Texas, during the Depression. No electricity, but they did have a battery-powered radio. And if you want to figure out where George Jones' voice comes from, he'll tell you it all started there, drifting in over the static.

JONES: The only music we ever listened to out in the piney woods was Roy Acuff and the Grand Ole Opry. That was the only night of the week I was allowed to lay in the middle of the bed with mama and daddy, just long enough to hear Roy 'cause then I had to go back to bed.

(SOUNDBITE OF MUSIC)

ROY ACUFF: (Singing) What a beautiful thought I am thinking...

JONES: After that, along came Hank Williams.

(SOUNDBITE OF MUSIC)

HANK WILLIAMS: (Singing) I'm so lonesome I could cry.

JONES: And then, Lefty came along.

BLOCK: Lefty Frizzell.

JONES: And he was so different, you know.

(SOUNDBITE OF MUSIC)

LEFTY FRIZZELL: (Singing) Always late with your kisses.

JONES: My lord, he'd take a word and twist it around and the way he would do that phrasing, that just tore me up.

BLOCK: George Jones was 22 when he got his first record deal. It was 1954, Starday Records in Beaumont, Texas, with producer Pappy Daily.

JONES: Pappy Daily came in there and said, George, I've heard you sing like Roy Acuff, Hank Williams, let's see, Lefty Frizzell, I just want to know one thing. Can you sing like George Jones? I said, well, I thought you wanted to sell some records.

(SOUNDBITE OF MUSIC)

JONES: (Singing) Find myself another 'cause there ain't no money in this deal. I mean it, baby, there's no money in this deal.

BLOCK: Whatever it is, the alchemy of Roy, Hank and Lefty mixed with his own wrenching ache, George Jones can pull and bend notes till they make you hurt. Listen to him drape his voice here.

(SOUNDBITE OF MUSIC)

JONES: (Singing) Just because I hang her number by mistake today, she thinks I still care.

BLOCK: It often sounded like George Jones was singing through clenched teeth, as if holding back the pain. And there was plenty of that - decades of hard drinking, drug addiction, violent rages.

(SOUNDBITE OF MUSIC)

JONES: (Singing) He embarrasses his child and his wife. Lord, he leads a miserable life. But still he thinks the bottle is his right hand.

BLOCK: There was bankruptcy, rehab that failed, marriages that failed, most famously with his longtime singing partner, Tammy Wynette. All the hard stuff filtered into his songs.

JONES: I'm crazy over a ballad, you know, one that's got a story and it's different, you know, from something you've heard before.

BLOCK: Which brings us to this, a song about unrequited love taken to the grave.

(SOUNDBITE OF SONG "HE STOPPED LOVING HER TODAY")

JONES: (Singing) He said, I'll love you till I die. She told him, you'll forget in time. As the years went slowly by, she still preyed upon his mind.

BLOCK: After George Jones finished recording this song, he told producer Billy Sherrill it was too morbid.

JONES: I said, Billy, I love the song, but I said, it ain't going to sell. It's too sad. But anyhow, how wrong could one person be? That turned out to be the signature song of my whole entire career.

(SOUNDBITE OF SONG "HE STOPPED LOVING HER TODAY")

JONES: (Singing) He stopped loving her today. They placed a wreath upon his door. And soon they'll carry him away. He stopped loving her today.

BLOCK: When people think of George Jones songs, a lot of time as being songs about heartbreak, songs about pain.

JONES: Yeah, it's not that you're unhappy when you're doing a ballad, it's just that I try to live the song. During that three minutes or whatever it is, oh, lord, you know, you try to step in that person's shoes. It seems, for some reason, the words tell you right away that you know how they feel.

BLOCK: Well, Mr. Jones, it's been a pleasure. Thank you so much for letting us come visit you.

JONES: Thank you all for being so nice. I do appreciate very much you all coming.

BLOCK: That's George Jones from our visit in 2010 at his home in Franklin, Tennessee. George Jones died today at age 81. I'm Melissa Block.

(SOUNDBITE OF SONG "THE RACE IS ON") Transcript provided by NPR, Copyright NPR.